1. Ground Resistance Measuring Instrument Wenner's Four-Electrode Method
The four (①, ②, ③, and ④) electrodes are lined up at regular intervals (a) and at a certain depth (d), and then an AC current is applied to the electrodes (① and ④) in order to measure the current value (I). The voltage (V) measured at electrodes ② and ③ is measured to obtain the resistance (R), which is calculated by the following formula.
2. Ground Resistance Measuring Instrument Kurash Bridge Method
By placing three electrodes in a triangle and measuring the resistance between each electrode.
3. Ground Resistance Measuring Instrument Voltage Drop Method
The potentiometer method cannot be applied to grounding systems that require a low value of ground resistance (e.g., a substation) or grounding systems that have a grounding network over a large area. Therefore, the voltage drop method is mainly used to measure the ground resistance of grounding systems such as network grounding. The voltage drop method, which measures the voltage drop by installing an auxiliary electrode at a certain distance from a point that is regarded as a point in the grounding area to be measured, has a small error.
The following points should be noted when applying this method.
In order to avoid the error caused by the voltage auxiliary resistance, a high impedance voltmeter should be used, such as vacuum tube voltmeter.
The induced voltage to the voltage circuit can be reduced by setting a bridge difference of 90° or greater between the voltage and current circuits.
When the current circuit power supply grounds one wire or zero, be sure to isolate the current circuit from the power circuit by means of an insulating transformer.
The distance between the voltage and current auxiliary electrodes should be adequate.
Since no current flows through the voltage circuit, the measurement path should be constructed to minimize induced voltages due to coupling between the voltage circuit and other circuits or current electrode wires, and errors due to the effects of ground currents and ground drift potentials should be eliminated.
Respondent: Huatian Power